1. Field of the Invention
The present invention relates to a fuel injection valve for injecting fuel by turning the flow of fuel in valve body to swirling flow.
2. Description of the Prior Art
In recent years, engines of intra-cylinder (direct injection) type are used in practical application, which inject fuel directly into engine cylinder in order to reduce fuel cost, to attain low emission and to provide higher output. In the fuel injection valve used in the engine of intra-cylinder injection type, fuel sent from a high pressure fuel pump is spirally fed into fuel injection chamber of semi-spherical shape and it is injected by increasing kinetic energy of the fuel in order to promote atomization of injection fuel.
To further improve atomizing performance of the fuel in this type of fuel injection valve, special notice was taken in JP-A-8-296531 that swirling energy of the fuel in a fuel injection chamber reaches maximum at the center of the bottom surface of the fuel injection chamber, and it was proposed to form an injection nozzle at the center of the bottom surface of the fuel injection chamber and to effectively utilize the swirling energy of the fuel for atomization.
In the fuel injection valve of the above patent application, direction of the injection nozzle formed at the center of the bottom surface of the fuel injection chamber is tilted with respect to axis of the fuel injection chamber to effectively utilize the swirling energy of fuel in the fuel injection chamber and to increase degree of freedom in the direction of the atomized fuel. For this reason, when the swirling flow of fuel in the fuel injection chamber enters inlet of the injection nozzle, flow velocity distribution of the fuel in axial direction of the injection nozzle is deviated. The deviation of flow velocity distribution of fuel is corrected to a certain extent by viscosity of the fuel itself during the course of flow in the injection nozzle, but it cannot be corrected perfectly. Therefore, the fuel is injected through outlet of the injection nozzle while deviation of flow velocity distribution of fuel still remains. This causes unevenness of the atomized fuel and decreases combustibility.
Specifically, atomized fuel is formed not in conical shape but in a shape of a cone obliquely cut. When atomized fuel is formed in such shape, on a portion where flow velocity of atomized fuel is slow, the atomized fuel does not reach near an ignition plug after injection and before ignition of the ignition plug, and it is not possible to collect air-fuel mixture with a concentration high enough compared with the surrounding atmosphere near the ignition plug in the combustion chamber at the time of ignition, and this hinders reduction of fuel cost.